The present invention relates generally to electrical contact devices and associated fabrication methods and, more particularly, to electrical contact devices for making electrical contact between electrical leads embedded within composite structures and related fabrication methods.
Composite structures are employed in an increasing number of applications, such as a variety of automotive and aviation applications. Regardless of the particular application, composite components can be formed by laying up or stacking a number of plies, such as on a tool or mandrel which, at least partially, defines the shape of the resulting composite structure. The plies are thereafter consolidated, such as by an autoclave process, into an integral laminate structure.
In addition to conventional autoclave processes, composite components can be fabricated by a fiber placement process in which plies of fibrous tow pre-impregnated with thermoset or thermoplastic resin, typically termed prepregs, are individually placed on and consolidated to an underlying composite structure. Preferably, a laser heats the lower surface of the fiber-placed ply and the upper surface of the underlying composite structure to at least partially melt a localized region of the ply. Compactive pressure is then applied to the at least partially molten region of the ply, such as by a roller disposed downstream of the laser, so as to consolidate the fiber-placed ply and the underlying composite structure, thereby forming the integral laminate structure. One advantage of a fiber placement process is that the composite material can-be cured on the fly, thereby reducing the time required to fabricate a composite part.
Another method of fabricating composite components is a resin transfer molding (RTM) process. According to a RTM process, a number of fibers, such as graphite or glass fibers, are woven to form a woven fiber intermediate structure. For example, the fibers can be woven on a loom-type structure as known to those skilled in the art. Resin can then be introduced to the woven fiber intermediate structure such that, once the resin has cured, the resulting composite component formed from the resin-impregnated woven fiber structure is created.
An emerging area of interest with respect to composite structures involves the design and development of smart structures. Smart structures generally refer to composite structures which include one or more interactive electronic devices. For example, monolithic or multi-layer electroceramic actuators can be embedded within a composite structure so as to induce vibrations within the composite structure. In particular, an electroceramic actuator can induce vibrations in the composite structure in order to offset or damp externally induced vibrations of the composite structure. In addition, smart structures can include other electrical devices, such as antennas and integrated circuits.
Even if the electrical device withstands the fabrication process, including the relatively high temperatures and relatively high pressures to which the device is exposed during consolidation, the electrical device must still be able to receive, and in many instances, transmit signals in order to function as desired. Accordingly, the embedded electrical device, such as an electroceramic actuator, typically includes a pair of electrical leads which are routed to the surface or edge of the resulting composite structure in order to provide for an external electrical connection, such as with an electrical lead extending outwardly from another composite structure.
A composite structure generally includes inner and outer surfaces through which the electrical leads of the embedded electrical device extend. In order to facilitate connection with other electrical devices, the electrical leads are typically routed through the inner surface of the resulting composite structure. Accordingly, troughs or bores must be formed or cut in the composite structure, such as from the interior surface thereof, so that the electrical leads can extend therethrough.
However, the surface egress of the electrical leads of an embedded electrical device is primarily effective in instances in which a hollow composite structure is fabricated, such as a trapezoidal rail, which permits the electrical leads to be routed to the hollow interior of the composite structure. In contrast, in instances in which the composite structure is not hollow, such as a solid or a relatively planar composite structure, the surface egress of the electrical leads of the embedded electrical device is less effective since the electrical leads will protrude from a surface, such as the exterior surface, of the composite structure and may interfere with the performance of the structure. In addition, electrical leads which protrude through the edge surface of one composite structure may obstruct or otherwise interfere with the alignment and interconnection of adjacent composite structures since adjacent composite structures must generally be brought into contact along the edge surfaces thereof.
Thus, the electrical leads typically extend into and are disposed within the hollow mandrel in a random order. Consequently, the electrical leads can become entangled with other electrical leads or with other surface-egressed components, such as optical fibers, to form a tangled web which is relatively difficult to disentangle. In addition, the electrical leads which extend into the hollow mandrel can sever other surface-egressed components, such as optical fibers, and can render repair of the components difficult, thereby impairing the performance of the resulting composite structure.
As a result of manufacturing or other limitations, a number of composite structures must oftentimes be mechanically joined in order to form even larger composite structures. As described above, electrical leads typically extend through many of the composite structures in order to interconnect actuators and other electrical components embedded within the composite structures. In addition to mechanically joining the composite structures, the electrical leads extending from a respective composite structure must therefore be connected to corresponding electrical leads extending from another composite structure.
In order to make the necessary electrical connections, the electrical leads of a conventional smart structure must first be disentangled. As will be apparent, the disentanglement of the electrical leads is a time consuming and tedious process. Once disentangled and connected, care must be taken to insure that the interconnected electrical leads are insulated from the composite structure which is itself at least partially electrically conductive. In addition, the interconnected electrical leads must be stored or located in a manner which does not impede the mechanical connection of the composite structures or the performance of the resulting structure. Therefore, even though the electrical leads extending from a number of individual composite structures can be interconnected, conventional techniques suffer from a number of deficiencies, including the time consuming and tedious nature of the interconnections, as described above.
As described in copending U.S. patent application Ser. No. 08/473,098 (the ""098 application) filed Jun. 7, 1995, the contents of which are expressly incorporated in their entirety herein, a composite structure having one or more embedded electrical components is described. The composite structure of the ""098 application includes a number of conductive tubes embedded within the composite structure that are connected to a respective electrical lead at one end and that open through an edge surface at the other end. Accordingly, electrical contact can be established with an electrical lead and, in turn, with the embedded electrical component from which the electrical lead extends by plugging a pin-like connector into a respective tube. Although the composite structure described by the ""098 application is a great advance in the art, precise alignment is required in order to interconnect the electrical leads embedded within a pair of adjacent composite structures since the same pin-like connector must be inserted into a respective tube from each composite structure.
It is therefore an object of the present invention to provide an electrical contact device for establishing electrical contact with an electrical lead embedded within a composite structure without requiring the electrical lead to extend through the surface or edge of the composite structure, thereby eliminating tangled electrical wires and the resulting time and difficulty associated with disentangling the electrical leads prior to establishing electrical connection.
It is another object of the present invention to provide for simultaneous electrical contact to be established between the electrical leads embedded with a pair of composite structures upon joining the composite structures.
These and other objects are provided, according to the present invention, by an electrical contact device for establishing electrical contact with a tubular electrical port opening through an edge surface of a composite structure. The electrical contact device includes a contact pad having opposed inner and outer surfaces. The outer surface is formed of an electrically conductive material, while the inner surface is formed of an insulating material, such as an epoxy. The electrical contact device also includes an electrically conductive pin attached to and extending outwardly from the electrical contact pad such that the pin is in electrical contact with the outer surface of the pad. Upon insertion within a tubular electrical port that opens through the edge surface of a composite structure, the pin serves to establish electrical contact between the tubular electrical port and the conductive outer surface of the contact pad, while the insulative inner surface serves to insulate the electrical contact device from the composite structure.
In order to improve the electrical performance of the electrical contact pad, the electrical contact pad of one advantageous embodiment includes a metallic substrate having inner and outer surfaces and a coating on the outer surface that has a greater electrical conductivity than the metallic substrate. For example, the metallic substrate can be formed of stainless steel and the coating can be formed of copper, nickel, gold or alloys thereof. The electrical contact device can also include an extension arm formed of a conductive material and extending outwardly from the outer surface of the electrical contact pad in order to further improve its electrical contact with another electrical contact device.
The pin is also generally formed of the same material as the metallic substrate, such as stainless steel. The pin is also preferably sized to have a diameter that is no larger than the inner diameter of the respective tubular electrical port. Typically, the pin has a diameter that is within 10% of the inner diameter of the respective tubular electrical port.
Typically, the composite structure is a multi-ply laminate structure having an edge surface and an electrical lead extending at least partially through the laminate structure. This composite structure also includes at least one embedded tube. A first end of the tube electrically contacts the electrical lead, while the second end of the tube opens through the edge surface to define an electrical port. By inserting the pin into the electrical port, electrical contact is established with the electrical lead.
By employing the electrical contact devices of the present invention, a pair of composite structures can be joined in such a manner that electrical leads embedded within the respective composite structures can be readily interconnected. In this regard, the pins of a number of electrical contact devices are initially inserted into respective tubular electrical ports of the pair of composite structures. By subsequently aligning the edge surfaces of the pair of respective composite structures, corresponding contact pads of each respective composite structure are also aligned and brought into contact, thereby establishing electrical contact between corresponding electrical leads embedded within the pair of composite structures. Consequently, simultaneous electrical and mechanical contact can be established between the electrical contact devices extending from the edge surface of one of the composite structures and corresponding ones of the electrical contact devices extending from the edge surface of the other composite structure.
The present invention also provides a method of fabricating a plurality of electrical contact devices. This advantageous method initially attaches a plurality of conductive pins to a strip of conductive material such that the pins are spaced along the conductive strip. According to one embodiment, holes are formed at a number of locations spaced along the strip. Conductive pins are then inserted through respective holes and bonded to the conductive strip. The strip of conductive material is then divided between each of the conductive pins to create a plurality of electrical contact devices.
The strip of conductive material preferably includes an outer surface and an opposed inner surface from which the pins extend. In order to isolate the conductive strip from the edge surface of a composite structure, an insulating material is typically applied to the inner surface of the conductive strip. In addition, the outer surface of the conductive strip can be coated with a conductive material having a greater electrical conductivity than the strip.
As a result of the construction of the electrical contact devices of the present invention, electrical contact can be readily established between corresponding electrical leads embedded within a pair of composite structures. Once inserted into a respective port, the pin makes electrical contact with one of the embedded electrical leads, while the remainder of the electrical contact device is electrically isolated from the edge surface of the composite structure. By appropriately aligning the edge surfaces of a pair of composite structures, electrical and mechanical contact can be simultaneously established between one or more pairs of electrical contact devices, thereby making electrical contact between corresponding electrical leads embedded within the composite structures without requiring the electrical leads to extend outwardly from the composite structure and to be individually interconnected.